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Bài 1: Cho A = 2-5+8-11+14-17++98-101 a, Viết dạng tổng quát dạng thứ n A b, Tính A Bài 2: Tìm x,y,z trờng hợp sau: a, 2x = 3y =5z x y =5 b, 5x = 2y, 2x = 3z xy = 90 c, y + z +1 x + z + x + y = = = x y z x+ y+z Bài Cho a a a1 a2 a3 = = = = = (a1+a2++a9 0) a2 a3 a4 a9 a1 Chứng minh: a1 = a2 = a3== a9 Cho tỉ lệ thức: a +b +c a b +c b = a +b c a b c Chứng minh c = Bài 4,5 : 47,375 26 18.0, 75 ữ.2, : 0,88 Thực phép tính: 17,81:1,37 23 :1 Tìm giá trị x y thoả mãn: x 27 2007 + ( y + 10 ) 2008 = Tìm số a, b cho 2007ab bình phơng số tự nhiên Bài Tìm x,y,z biết: x y z x-2y+3z = -10 = = Cho bốn số a,b,c,d khác thoả mãn: b2 = ac; c2 = bd; b3 + c3 + d3 3 Chứng minh rằng: a3 + b3 + c = a b +c +d d Bài Chứng minh rằng: 1 1 + + + + > 10 100 Tìm x,y để C = -18- x y + đạt giá trị lớn Câu ( 2đ) Cho: a b c Chứng minh: a + b + c = a = = b c d d b+c+d Câu (1đ) Tìm A biết rằng: A = Câu (2đ) a) A = a c b = = b+c a+b c+a Tìm x Z để A Z tìm giá trị x+3 x2 b) A = 2x x+3 Câu (2đ) Tìm x, biết: a) x3 = b) ( x+ 2) = 81 c) x + x+ = 650